1. Field of the Invention
The present invention relates to a metal plate stator case for radial centrifugal pumps.
2. Description of the Prior Art
Stator cases of this type are known in which an annular header is provided peripherally to the bladed impeller; said header is formed by a circular channel which has an approximately constant radial transverse cross section and has the function of collecting and conveying the output flow from the impeller toward an essentially radial discharge outlet. Since a diffusion element for converting part of the kinetic energy imparted to the fluid by the impeller into pressure energy is not provided inside said cases for the sake of constructive simplicity, the discharge outlet itself is shaped like a diffusion nozzle. For this purpose, the discharge outlet is constituted by a divergent duct which is designed so as to allow an adequate loss of speed and a corresponding increase in pressure.
Though on one hand it offers the advantage of considerable constructive simplicity, this solution on the other hand has some structural disadvantages which are observed during the operation of the pump. The flow collected by the annular header along its circumferential extension in fact increases progressively from a minimum value to a maximum one toward the discharge outlet and then suddenly drops back to the initial minimum value after said discharge outlet. The impeller is consequently subjected to considerable periodic stresses which are equal in frequency to the rotation rate of the pump; these stresses cause early breakage due to fatigue and produce considerable noise. Stator cases of this type are furthermore characterized by a excessive size due to the considerable length of the diffusion and discharge nozzle.
In order to obviate the above described disadvantages, it has been proposed to make metal plate stator cases provided with a spiral-shaped volute similar in design to monolithic stator cases obtained by casting. However, the manufacturing of these types of volute is still rather expensive due to the large number of component parts or to the use of complicated and expensive pressing methods.
The aim of the present invention is to eliminate or at least significantly reduce the disadvantages described above by providing a metal plate stator case, particularly for centrifugal radial pumps, which is highly reliable and has a reduced cost.
Within the scope of the above described aim, a particular object of the present invention is to provide a metal plate stator case which has a diffusion volute which is functionally equivalent to those obtained by casting.
Not least object of the invention is to provide a metal plate stator case which can be easily obtained by pressing starting from commonly commercially available materials.